Fall Index Netting – Overview

Background

"How are the fish in my lake doing?" We need this answer to set management objectives and appropriate fishing regulations, to understand and correct any problems with fish habitat, and to guard against invasive species.

A healthy fish population and fish community means we can all enjoy the benefits of sustainable fisheries and healthy ecosystems. A standard method of assessing the status of fish populations is necessary to allow comparisons of fish sustainability across the years at a lake, and to compare to other lakes.

We use a North American accepted standard of index netting for lake fisheries assessment (Morgan, 2002). This method provides the necessary data on fish abundance, biological data (such as age and gender), and species diversity to assess sustainability.

These data, along with other information, supports assessments of fishery sustainability, and along with the Fisheries Management Objectives for a fishery, are used to determine the most appropriate sport fishing regulation. These assessments allow for consistent comparisons of fish sustainability and status between populations over time.

What is Fall Index Netting (FIN)?

Fall index netting is used by the Alberta government to primarily monitor Walleye and Northern Pike populations.

Fall index netting typically occurs during late summer and fall when water temperatures are between 10 and 15 °C, when fish are known to be more evenly distributed within the lakes.

Standardized multi-mesh gill nets are set at random locations between 2 and 15 metres deep, set for 21-27 hours (for example: a net-night), and then reset in new random locations the next day. A half-length variation of the standard index net is sometimes used, balancing precision of the catch rates with reduced sampling effort.

Sampling effort is proportional to lake size, so larger lakes can require more nets. Information from Yellow Perch, Lake Whitefish, Burbot, minnow and sucker species are also collected. The information collected from each fish includes length, weight, age, gender, and maturity.

How is this information used?

Catch rates (for example: number of fish captured per net-night) of Walleye and Northern Pike are a measure of the population's abundance, with higher catch rates meaning there are more fish in the lake.

The abundance of adult fish is compared to the standardized thresholds for 5 broad categories of risk to the long-term sustainability of the fish population, with higher densities of fish having lower risk (Table 1).

The sizes and age of fish also tell us if problems with overharvest (for example: too few fish living to old age) or habitat (for example: poor spawning success) are a concern. Biologists use this information, as well as a variety of data on water quality, access, development, and habitat threats as part of Alberta's Fish Sustainability Index (FSI).

These assessments as well as the Fisheries Management Objectives are used to determine the most appropriate sport fishing regulations for a lake. This landscape-level assessment allows for consistent, broad temporal comparisons of fish sustainability and status.

For more information on fish conservation and management in Alberta please see:

• Fisheries Conservation and Management Strategy
• Fish Sustainability Index

Table 1 - Alberta's Fish Sustainability Index risk thresholds for Walleye and Northern Pike using the standardized Fall Index Net (FIN) method.

Frequently Asked Questions (FAQs)

What is CUE (Catch per Unit Effort)?

Catch per unit effort (CUE) refers to the catch of fish by a specified method. The method is standardized by a unit of effort so it provides a sound basis for comparison amongst fish populations.

For fall index netting (FIN) survey, the unit of effort is a net-night, which represents one standardized gill net, set on average for a 24-hour period.

Typically, the FIN catch rate is reported as the average for the survey at a lake. So, a FIN CUE of 10 Walleye per net-night means that an average of 10 fish were captured per net per 24 hours (or 10 Walleye/net-night).

How many walleye and pike are in a lake?

Abundance is the number of fish per area (or fish/hectare) and can be used to estimate the number of fish in a lake population. FIN catch rates (or CUE) of Walleye and Northern Pike are related to their abundance. However, higher catch rates of one species compared to the other does not necessarily mean they are in higher abundance.

Walleye and pike are not equally vulnerable to being caught in a FIN gill net. Interestingly, Walleyes are more vulnerable than pike to being caught in FIN gill nets. This is because of biology, where they typically reside in a lake, and increased foraging activity because of our northern climate.

Therefore, when a FIN survey catches more Walleyes than pike, counterintuitively, the abundance of Walleyes in the lake may be lower than the abundance of pike (see Table 2 for examples).

Table 2 - Examples of FIN catch rates adjusted for abundance. These adjustments are from Mogensen, Post and Sullivan 2013.

Are FIN results valid for other species?

Fall index nets catch the species of fish that are vulnerable to the index netting method. Biological data are collected from all fish that are captured.

Catch rates of fish species (for example: Walleye / net-night) are calibrated to the abundance of those species.

A common method is to calibrate catch rates to other indexes of abundance for example catch rates from creel surveys or population estimates conducted using various mark and recapture methods.

How many fish are killed during a FIN assessment?

FIN assessments do kill fish. The FIN is very effective in assessing the status of Walleye and other species like Northern Pike.

Every effort is made to limit fish mortality by understanding how many fish are required to make an accurate assessment and planning the survey accordingly.

The number of nets set each day is limited so the catch can be closely monitored and once sufficient data is collected the survey is concluded; usually 100 to 200 fish are collected.

After sampling, if fish are appropriate for human consumption, Alberta biologists are required to provide the fish to local Indigenous peoples or to persons on approved subsistence lists. Typically, a tiny proportion of the lake's fish population (usually less than 1 or 2%) are killed in this sampling.

Are there other methods to assess fish stocks that provide similar information as FIN?

Generally no...FIN assessments do a very good job at estimating the abundance, structure (i.e., age and length-classes) and the health (for example: gender, age-at-maturity) of a fish population.

Other methods do a good job; however, the questions they answer are different from the questions a FIN survey answers.

For descriptions of assessing fish populations and fisheries, please see Alberta's Fish Conservation and Management Strategy:

• Alberta's Fish Conservation and Management Strategy

Other fisheries methods include:

• Electrofishing on a lake is typically used to collect fish for a population estimate when fish are concentrated during spawning season. This method is favoured when working on flowing waters of a variety of sizes.

• Angler surveys (also referred to as creel surveys) collect information directly from sport anglers. The sport anglers' catch rate (for example: number of fish caught per angling-hour) is related to the abundance of fish.

  Angler surveys also provide opportunities to collect demographic information from anglers and biological information from their harvest.

  However, regulations that limit the harvest of fish also limit the opportunity to sample fish for length, weight, age, gender, and maturity.

  Angler surveys also provide the outreach opportunities to discuss common fisheries management topics with anglers. Angler surveys are fairly costly, due to the amount of man-hours required to complete the survey.

• Sample angling involves staff and volunteers angling to collect biological data from fish before they are released. Sample angling can be the best way to sample a population in remote locations.

  An adequate sample can be challenging to attain though and participating anglers' catch rates are not an index of abundance; therefore, sample angling is best used to augment other assessments (for example: angler surveys).

  Sample angling provides the opportunity to engage stakeholders and involve them in management related activities.

• Live trapping fish in lakes is similar to electrofishing. Trapping is conducted where and when fish are concentrated and readily-catchable (for example: spawning season).

  Fish can be counted, measured, sampled, tagged for tracking studies, or eggs and milt collected for stocking activities.

  Traps, however, do not provide useful estimates of abundance (for example: fish/area) or a sample of immature fish.

• Population estimates are typically done using a mark-recapture approach. Fish are captured when naturally concentrated, marked, released, allowed to mix with the unmarked population and recaptured at a later time.

  The ratio of marked compared to unmarked fish in the overall catch provides an estimate of the population size.

• Movement studies or telemetry answers questions about the biology and habitat use of fish during certain times of year.

• Genetic studies can be used to describe the boundaries of a population as well as ecologically-significant species, strains and races of a fish.

  Genetic information is important for the development of restorative stocking strategies, conservation and management plans.

FIN is a very effective, efficient, and affordable tool that provides an unbiased assessment of Walleye and Northern Pike populations.

Before a regulation can be changed on a lake, does the Fisheries Management Branch need to complete a FIN?

No, not necessarily. Fisheries Management Branch needs to base management and regulations on a sound understanding of the status of a population.

Depending on the circumstances, biologists will propose and implement a change to management objectives and regulations in the absence of FIN data, based on other events (such as a fish kill) or information (for example: new road access to a remote lake).

Regulations are aimed at specific outcomes and undergo internal scientific review. Consultation with stakeholders (anglers, First Nations, etc.) regarding Fisheries Management Objectives (for example: the desired state of a fishery) is an important component of managing Alberta's fisheries.

Is gillnetting used by other governments?

Yes! Fall (Walleye) Index Netting method was rigorously evaluated and developed in Ontario and was adopted in Alberta in 2000. Alberta validated the method and ensured 1) the catch rates (fish/net-night) are highly correlated to abundance (fish/ha) and 2) the biological sample accurately represents the population structure.

Under various names and by many agencies, standardized index-netting is used as a fish population assessment tool around the globe. Examples include;

• The large mesh gill net (aka North American Gear) is supported by the American Fisheries Society (Bonar et al., 2009)
• The Nordic gang was developed in Norway and adopted in Europe (Appleberg, 2000) and the
• Ecological Framework for Fisheries Management (EFFM) was adopted in Ontario by the Minister of Natural Resources (Sandstrom et al., 2013).